The only dumb question is the one that doesn't get asked. The 604 is just a 604. The Lawn Rangers were (believe it or not) smaller units with smaller tires on the front and rear. I don't know the specific sizes, but the rears were maybe 8" or 10" and the fronts were like a 4" or 6". They're tiny is all I know for sure. There's one in this picture from the Wheel Horse show. It's the second from the left.

Lawn Rangers aren't actually smaller, they are just lower because of the smaller tires/wheels.
Aside from the obvious smaller wheels/tires, many of the parts will interchange between the early (1962 to 1964) Lawn Rangers and the regular garden tractors of the same time period.
The '65 to '68 Lawn Rangers did have a unique (to them) hoodstand, rear fender, etc., but they are still based on the standard 41.5" wheelbase round hood garden tractors.